An integrated circuit, such as a processor circuit, produces heat in a circuit die or substrate. Failure to efficiently remove the heat from the die results in failure of the circuit. One method of removing heat from a die includes thermally coupling a finned heat sink to the die and forcing air across the fins using a fan. Unfortunately, forced air cooling is not practical for cooling integrated circuits in hand held communication devices or in personal digital assistants. In addition, forced air cooling has a number of significant disadvantages, even when used in cooling systems, such as servers and engineering workstations, that have traditionally used forced air cooling.
One disadvantage associated with forced air cooling is that it is expensive. Customers who purchase systems composed of integrated circuits, such as computers, are interested in reducing the operating costs of those systems. A fan moves air by driving a fan blade with a motor. The motor requires energy to operate. Using a fan to provide forced air cooling in these systems increases the operating costs of the systems.
As the circuit density on a die increases, more heat is produced on the die and the die needs to be cooled quickly to avoid circuit failure. To cool the die quickly, the rate at which air is forced across the heat sink is increased. Increasing the rate at which air is forced across the heat sink generally requires a fan having a larger blade and a larger motor. The larger motor consumes more power and increases the system operating costs.
Another significant disadvantage associated with forced air cooling is that it is not effective for cooling hot spots on a substrate. Heat is not generated uniformly over the surface of an integrated circuit substrate. This uneven generation of heat produces hot spots in the substrate. In some systems, hot spots may be cooled sufficiently to prevent immediate catastrophic failure of the circuit using forced air cooling, but over time, failure to adequately cool hot spots leads to premature failure of the circuits fabricated near the hot spots.
For these and other reasons there is a need for the present invention.